Q. The first U.S. baby born with brain damage caused by the mosquito-borne Zika virus was reported last week in Hawaii. How concerned should pregnant women in the United States be?

A. When pregnant women contract Zika, the baby can be born with microcephaly, a congenital condition associated with an underdeveloped head and brain. The Hawaii mom is reported to have been infected in Brazil in...

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Q. The first U.S. baby born with brain damage caused by the mosquito-borne Zika virus was reported last week in Hawaii. How concerned should pregnant women in the United States be?

A. When pregnant women contract Zika, the baby can be born with microcephaly, a congenital condition associated with an underdeveloped head and brain. The Hawaii mom is reported to have been infected in Brazil in 2015, where there has been an uptick in birth defects caused by Zika, says Erin Sykes of the U.S. Centers for Disease Control and Prevention press office.

No cases have been contracted in the United States, Sykes says, although Zika has been reported in Puerto Rico. “There’s no reason for concern here,” Sykes says. The woman and baby in Hawaii are not infectious, she says.

Zika is transmitted by the Aedes aegypti species of mosquitoes. They aren’t found in New York, but they are in Texas, Florida and elsewhere in the Southern United States;

For the virus to take root here, an already actively infected person would have to enter the country, be bitten by a mosquito, and that mosquito would have to bite other people, she says.

That scenario is extremely unlikely, says Dr. Sharon Nachman, division chief of pediatric infectious diseases at Stony Brook Children’s Hospital. “You need a critical mass of mosquitoes jumping from person to person and a critical mass of people who are contagious over long periods of time,” Nachman says.

The CDC is following developments, so Sykes suggests women stay in touch with their obstetricians on the issue. In “an abundance of caution,” the CDC has advised pregnant women not to travel to areas where Zika has been linked to serious birth defects, including Brazil, Colombia, El Salvador, French Guiana, Guatemala, Haiti, Honduras, Martinique, Mexico, Panama, Paraguay, Puerto Rico, Suriname and Venezuela. Zika is not uncommon in parts of South and Central America and the Caribbean, Nachman says. It’s normally a mild virus whose symptoms include fever, rash and joint pain, but it can affect a fetus, she says. There’s no vaccine or treatment, according to the CDC.